onsdag 3 oktober 2012

The Enigma of the Airfoil 2

The Enigma of the Aerofoil: Rival Theories in Aerodynamics 1909-1930, by David Bloor, 2011, describes the initial British criticism of the German circulation theory of lift developed by Kutta and Prandtl in the beginning of the 20th century, which resisted the attack in the absence of something better and became the leading theory propagated in text books still today. From the description of the book:

Why do aircraft fly? How do their wings support them? In the early years of aviation, there was an intense dispute between British and German experts over the question of why and how an aircraft wing provides lift. David Bloor ... reveals the impact that the divergent mathematical traditions of Cambridge and Göttingen had on this great debate.

It is illuminating to read the book from the perspective of the New Theory of Flight, which explains the real physics of generation of lift and drag of a wing resulting from a specific instability mechanism of potential flow, and in particular shows that the circulation theory is unphysical and thus incorrect.

Bloor says about English skepticism to German circulation theory:

Horace Lamb had also made gentle fun of the theory of circulation by exploiting the theological overtones of Kelvin's theorem. In his Rouse Ball Lecture of 1924, titled "The Evolution of Mathematical Physics", Lamb had said of perfect fluid theory that "this theory cannot tell us why an aeeroplane needs power for its propulsion; nor, indeed, can it tell us how the aeroplane obtains its sustenation, unless by assuming certain circumstances to have been established at the Creation which, in all reverence, we find it hard to believe" (circulation).

Every takeoff and landing, Lamb hinted, would require divine anticipation and intervention (circulation).

In the last edition of his Hydrodynamics, in 1932, Lamb returned to the problem of the origin of circulation and of understanding how it resulted from a smooth flow being established at the trailing edge of a wing. He clearly felt that no satisfactory account had been given of this (circulation).

Bloor describes how English wit outmaneuvers German technocracy, in what can be seen as an anticipation of the upcoming war. Germany lost the war but German circulation theory survived in the absence of anything better.